Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuits often include a power amplifier for driving an audio output signal to the headphones or speakers, wherein the power amplifier itself is driven by a pre-amplifier (e.g., a digital-to-analog converter). In many implementations, the pre-amplifier and the power amplifier are supplied from different, isolated power supplies.
In such scenarios, the amplitude of an audio output signal may be directly proportional to the power supply of the pre-amplifier, and may thus vary as the power supply of the pre-amplifier varies (e.g., due to noise or other parasitic effects affecting the power supply). Because the power supply of the power amplifier is uncorrelated from the amplitude of the pre-amplifier output signal driving the power amplifier, conditions may from time to time exist in which the power amplifier power supply does not provide enough voltage headroom for the audio signal, leading to clipping or other distortion of the audio signal.